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  • Nitrogen absorption...

    As a PADI SCUBA Instructor, each new Bering Sea gold rush season has sends a few questions my way about the dredging they do. Specifically, how long they stay underwater before going past NDL (no decompression limit). So I thought I'd post the answer here for everyone who is interested.

    It is common for dredgers to claim you don't have to pay attention to dive tables until you go past 10 meters. That is 100% incorrect. You cannot change physics no matter how much you may not like/comprehend physics. Physics tells us nature seeks equilibrium. So as soon as your body goes below the surface when SCUBA diving, you are absorbing excess nitrogen. Again, you can't change physics.

    The confusion seems to arise due to dive tables starting at 10 meters. People assume any depth less than that and you don't have to worry about it. What they are forgetting (or never learned if they never got SCUBA certified) is that the tables tell you to use 10 meters for ANY depth 10 meters or less.

    This is because when the Navy created the dive tables they could not distinguish any difference in nitrogen absorption between 0-10 meters. NOT that no nitrogen absorption takes place under 10 meters, just their measuring couldn't tell the difference in the amount of bubbles in the bloodstream. So you use the 10 meter dive table for any depth <= 10 meters.

    How long do you have at 10 meters before you hit NDL? About 3 hours. So when you hear of someone on that show staying under for 6/7/8/9 hours, they have in gone into decompression mode. Not maybe, they are definitely in decompression mode. Again, not believing/not comprehending it doesn't change physics.

  • #2
    Does that change when using surface supplied air?

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    • #3
      No, that does not change when using surface supplied air. For those who never heard of that diving method, instead of carrying an air tank you are connected via a hose to a compressor at the surface.

      The reason is because the air is delivered at ambient pressure you are diving at when you inhale, regardless of the delivery method.

      This does not apply to free diving where you hold your breath and dive. It only applies when breathing compressed air.

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      • #4
        You are kinda right. Yes you could use that as an average rule and be fairly conservative. However, in reality there's many more factors that were not mentioned. I've done 8 hours at 20ft of sea water to surface for 8+ hours many times. I never had decompression. Maybe you scuba guys do it differently. I was a hard hat diver for 16 years, what do I know!

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        • #5
          Originally posted by shayno View Post
          You are kinda right. Yes you could use that as an average rule and be fairly conservative. However, in reality there's many more factors that were not mentioned. I've done 8 hours at 20ft of sea water to surface for 8+ hours many times. I never had decompression. Maybe you scuba guys do it differently. I was a hard hat diver for 16 years, what do I know!

          You can't change physics. Physics tells us your body equalized the gases in your body with the pressure at 20ft of depth, or approximately 1.6 atm. It is more accurate to say you didn't realize you were in DCS. Symptoms are different for everyone and quite often they are either not recognized or ignored.

          You should have gone into a chamber to reduce the damage those bubbles may have caused when you surfaced and your body went into high gear to equalize back to 1atm. The bubbles and the potential damage will occur whether or not you believe in physics.

          On a side note, DCS damage is cumulative which is why we have the old scuba joke: "commercial divers don't die of old age".

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          • #6
            There is a Navy table 7-3 that starts at 10' which is in the neighborhood of where most of these guys are diving. 10' for 797 minutes makes you a E on the table. E is pretty safe and the reality is it's highly unlikely that these guys are actually spending all those hours non stop on the bottom regardless of what is said on the show. In fact, the table itself says you cannot get past an F no matter how long you stay on the bottom.

            Even if they were to spend 6 hours down and become a D, it's only 1:48 to get back to a B. Of course this isn't factoring in the cold and other factors like hydration and level of work, etc but in reality 6 hours at 10' is about the same as 25 minutes at 50'.

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            • #7
              Recreational dive tables use 10m as the basis for any dive <=10m because when they tested the volunteer Navy divers they could not see any difference in the microbubbles created at 1m vs 10m. So they wisely decided that the 10m numbers should be used for any diving <= 10m. Using the dive tables you reach NDL at 3 hours 22 minutes.

              There's no law saying you can't risk it and go beyond NDL. But I prefer to not play Russian roulette when I go diving and always err on the safe side.

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              • #8
                I have a side question. Anyone know what has been the deepest saturation dive in Alaska........???
                "Life Is Either a Daring Adventure or Nothing" - Helen Keller

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                • #9
                  Cheeser surely remembers that scuba divers, and those that are diving on surface-supplied air, are safe to remove up to one-half the atmospheric pressure under which they were diving.

                  The accepted USN dive tables, as shown in the U.S. Navy Dive Manual, were formulated by an old acquaintance of mine: Dr. Al Behnke. He was kind enough to autograph my personal copy.

                  I am certified as a Dive Instructor by NAUI, PADI, YMCA, and LA County. As an aside, Al and USN Commander Don Ferrin were both on the review board when I went through my NAUI Instructor's coarse.

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                  • #10
                    Originally posted by Grizzly 2 View Post
                    Cheeser surely remembers that scuba divers, and those that are diving on surface-supplied air, are safe to remove up to one-half the atmospheric pressure under which they were diving.

                    The accepted USN dive tables, as shown in the U.S. Navy Dive Manual, were formulated by an old acquaintance of mine: Dr. Al Behnke. He was kind enough to autograph my personal copy.

                    I am certified as a Dive Instructor by NAUI, PADI, YMCA, and LA County. As an aside, Al and USN Commander Don Ferrin were both on the review board when I went through my NAUI Instructor's coarse.

                    Your "remove 1/2 atm" was never part of my PADI instructor training nor have I ever heard any course director or instructor cite that. Please send a reference to that if you could as I'd be very interested in reading it.

                    Very cool about that autograph!! The stories I've read of the effort that was made and the risks those divers took was fantastic reading. It puts into perspective all of the work that was done and the risks that were taken so we can enjoy safe diving today.

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                    • #11
                      Originally posted by AGL4now View Post
                      I have a side question. Anyone know what has been the deepest saturation dive in Alaska........???
                      Around 545 foot. Monty McPherson did it back in the mid eighties. Took place in the gulf of alaska back in the day when they had a semi submersible drilling out there. I've worked with him for 15+ years.

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                      • #12
                        Originally posted by Cheeser View Post
                        You can't change physics. Physics tells us your body equalized the gases in your body with the pressure at 20ft of depth, or approximately 1.6 atm. It is more accurate to say you didn't realize you were in DCS. Symptoms are different for everyone and quite often they are either not recognized or ignored.

                        You should have gone into a chamber to reduce the damage those bubbles may have caused when you surfaced and your body went into high gear to equalize back to 1atm. The bubbles and the potential damage will occur whether or not you believe in physics.

                        On a side note, DCS damage is cumulative which is why we have the old scuba joke: "commercial divers don't die of old age".
                        Huh... Well no I cannot change physics. You sir (or ma'am) are correct. I'm pretty sure I can recognize myself if I was bent. I'm also pretty sure my body wasn't going into "high gear". Not really sure what that means.
                        Not sure what DCS damage is?
                        Here's the reality for ya. Its about to get real. Lol
                        Scuba divers are the ones who are at far greater risk for any type of diving related injuries. That's a fact. I've spent more time on a ladder (im slow lol) getting out of the water than most scuba divers have ever spent in the water, and I've never been bent. Out of 16 years of jobs, I saw not a single instance of someone getting sick. Is that the norm? Yes. Because we are very heavily regulated and it is our livelihood. Its taken seriously and when you've got a drill ship or a platform waiting on you to do your job, you cannot afford to play around with tables. That's why we carried around a chamber or two everywhere, so we can play with the big boy tables. (No offense)
                        As far as everything 40 fsw to surface goes, we just make the diver come up above 20 few to keep him from z-ing out. (Legitimately use the tables) We also used to do repets on sur-d-02's, that was something that always made me a lil uncomfortable, but still legal.

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                        • #13
                          Do you happen to know if the rig was the "Ocean Ranger".......??? We did a deep saturation dive for "Arco" off the "Ocean Ranger" roughly 1978 (I could be off a year). This was in the general Unlalaska/Dutch Harbor area. This was an "Active Dive Co." project.

                          Originally posted by shayno View Post
                          Around 545 foot. Monty McPherson did it back in the mid eighties. Took place in the gulf of alaska back in the day when they had a semi submersible drilling out there. I've worked with him for 15+ years.
                          "Life Is Either a Daring Adventure or Nothing" - Helen Keller

                          Comment


                          • #14
                            Originally posted by AGL4now View Post
                            Do you happen to know if the rig was the "Ocean Ranger".......??? We did a deep saturation dive for "Arco" off the "Ocean Ranger" roughly 1978 (I could be off a year). This was in the general Unlalaska/Dutch Harbor area. This was an "Active Dive Co." project.
                            Yes, I'm pretty sure it was the ocean ranger! The story as told to me was that it was in the gulf. But, I could have heard that part wrong. What's amazing is that 3 of those dive crew guys are still in the business, and 2 more retired about 8 years ago!

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                            • #15
                              Originally posted by shayno View Post
                              .........I'm pretty sure I can recognize myself if I was bent. ................ I've spent more time on a ladder (im slow lol) getting out of the water than most scuba divers have ever spent in the water, and I've never been bent.........
                              I've often wondered how a person explains how it feels to get the bends? I guess I've always assumed it being like getting one big ache, or charlie horse all over your body? What kind of pain is it like, or what a person could relate it to...??? Just curious....
                              Sheep hunting...... the pain goes away, but the stupidity remains...!!!

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